1. Field of the Invention
The present invention relates in general to a cycloaliphatic polyimide (or called polycyclic aliphatic polyimide or alicyclic polyimide) a method for producing the same, and its use. In particular, the present invention relates to a cycloaliphatic polyimide with heat-resistance, low dielectric constant, and high transparency.
2. Description of the Related Art
Polyimide is an important polymer in the microelectronics and photoelectronics industries. It is widely applied in photoresist, passivation or dielectric film, soft print circuit board, and optics film and alignment films of the display. The polyimide used in the photoresist is photosensitive, and can be patterned by photolithography and used to transfer the pattern into the underlayer. The photosensitive polyimide also can form the passivation or dielectric film with heat-resistant and corrosion-resistant characteristics. The thermosensitive polyimide is used in the fabrication of soft print circuit boards, optics film and alignment film. In general, the polyimide has the properties of heat-resistance, low dielectric constant, and high transparency, which are the trend of the future development.
The precursors of the polyimide resin are thermo-cured polyamic acids or photo-cured polyamic esters. The thermo-cured polyamic acid is formed by the polycondensation of aromatic dianhydride with aromatic diamine. If an acrylate is also added to react with the aromatic diamine and the aromatic dianhydride, the reaction, the radical polymerization, is initiated by light, after post-curing, to form the polyimide film.
In Japan patent 1181091 and U.S. Pat. No. 4,778,859, aliphatic or alkynyl sidechains, or ethylene glycol bis(3-aminopropyl) ether and diamino siloxane are introduced into the aromatic polyimide to reduce the inter-molecular charge-transfer interaction and enhance transmittance and solubility. However, the intra-molecular charge-transfer interaction cannot be reduced to prepare the thoroughly transparent polyimide film, and its thermal stability is insufficient.
In Japan patents 07018074 and 03188163, the fluoro-based compound is employed as the reactant. Although the optical properties of the resulting polyimide are improved, and its dielectric constant is reduced to 3.0, the cost is too high to have economic benefits.
It is an object of this invention to develop a new cycloaliphatic polyimide and the method for producing the same. Such cycloaliphatic polyimide is rigid and polycyclic, and it has the properties of thermal stability, thorough transparency and lower dielectric constant required for application in the microelectrics and optoelectrics industries.
Therefore, the present invention provides a cycloaliphatic polyimide with the following formula (I) 
wherein Cl, Cm and Cn can be alkyl or alkenyl, l is an integer from 4 to 7, n is an integer from 4 to 7, m is an integer from 0 to 2, and p is an integer from 1 to 8.
In such cycloaliphatic polyimide, cyclic aliphatic group R can be C1-8 cycloalkyl, cycloalkenyl, cycloalkynyl, norbornenyl, decalinyl, adamantanyl, or cubanyl.
The above-mentioned cycloaliphatic polyimide can be applied in photoresist, passivation film, dielectric film, optics film, and alignment film.
A polycondensation is proceeded by reacting the polycyclic aliphatic diamine having the following formula (II) with the polycyclic aliphatic dianhydride having the following formula (III) to form the product, polycyclic aliphatic polyamic acid or polycyclic aliphatic polyamic ester, having the following formula (IV). The product was converted to the cycloaliphatic polyimide having the following formula (I) when taking the cyclic reaction. 
wherein Cl, Cm and Cn can be alkyl or alkenyl, l and n are integers from 4 to 7, m is an integer from 0 to 2, p is an integer from 1 to 8, x is an integer equal to or greater than 1, cyclic aliphatic group R can be C1-8 cycloalkyl, cycloalkenyl, cycloalkynyl, norbornenyl, decalinyl, adamantanyl, or cubanyl, and Rxe2x80x2 can be hydrogen or acrylate group.
In the polycyclic aliphatic diamine having the following formula (II), the cyclic aliphatic group R can be C1-8 cycloalkyl, cycloalkenyl, cycloalkynyl, norbornenyl, decalinyl, adamantanyl, or cubanyl. A specific example is 1,3-diamino adamantane.
In such polycyclic aliphatic dianhydride having the following formula (III), the repeating unit of its cyclic aliphatic structure is a cyclic system constituted by two the same or different C4-7 alkyl or alkenyl, and C0-2 alkyl or alkenyl as a bridged group. Specific examples are bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and pentacyclo [8.2.1.4,702,903,8]tetradecane-5,6,11,12-tetracar-boxylic dianhydride.
The polycondensation and cyclic reaction depicted above are proceeded in polar aprotic solvent which can in general be 1-methyl-2-pyrrolidinone (NMP), N,N-dimethyl acetamide, tetrahydroxythiophene-1,1-dioxide, N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), tetramethyl urea, or xcex3-butyrolactone.
The polycondensated product (IV) can be thermo-cured polycyclic aliphatic polyimic acid or photo-cured polycyclic aliphatic polyamic ester. If Rxe2x80x2 is H, the product (IV) is the former. If Rxe2x80x2 is the acrylate group, the product (IV) is the latter.
In the preparation of the photosensitive cycloaliphatic polyimide, the acrylate is further added to take the polycondensation. The acrylate can be trimethylolpropane triacrylate (TMPTA), hydroxyethyl methacrylate (2-HEMA), hexanediol diacrylate (HDDA), hydroxyethylacrylate (HEA), pentaerytrithol triacrylate (PETA), ethyldiethyleneglycol acrylate (EDGA), tripropyleneglycol diacrylate (TPGDA), or pentaerytrithol tri and tetra acrylate (PETIA).
The method of taking the cyclic reaction to cure the product (IV) is thermopolymerization or photopolymerization. If Rxe2x80x2 is H, thermopolymerization is chosen to dehydrate and form the thermosetting cycloaliphatic polyimide under a temperature of about 0xcx9c400xc2x0 C., preferably under about 350xcx9c400xc2x0 C. If Rxe2x80x2 is the acrylate group, photopolymerization is chosen. An initiator is added and then exposed to uv/vis light to induce photopolymerization, forming the photosensitive cyclicaliphatic or cycloaliphatic polyimide. The initiator can be Michler""s ketone, tribromomethylphenyl sulfone (TBPS), 2,4-diethyl-9H-thioxanthen-9-one (DTX), isopropyl-9H-thioxanthen-9-one (ITX), 3-acetylcoumarin, 3,3-carbonylbis(7-diethylaminocoumarin), 2-methyl-4xe2x80x2-(methylthio)-2-mor-pholinopropiophenone, benzil(2-ethoxycarbonyl)monoxime, 2,6-bis(4-azidobenzyliolene)-4-methylcyclohexanone, N-(4-azidosulfonylphenyl)-maleinimide, 2-benzyl-2(dimethylamino)-4xe2x80x2-morpholinobutyrophenone, or 2,2-dimethoxy-2-phenylacetophenone.
According to the situation of Rxe2x80x2 being the acrylate group, a mask having a pattern thereon can be used in the above-mentioned exposure step with the exposure energy of about equal to or smaller than 100 mJ/cm2. The development step with a developer is followed to remove the unexposed parts to obtain the patterned cycloaliphatic polyimide film.
Without any intention of limiting itself in any way, the present invention is illustrated further by the following examples.